Significance

Our multidomain-corrected paleointensity results from near-equatorial lavas from the Galapagos give a mean intensity only about one-half of that obtained from the only robust published result from near-polar lavas from Antarctica. This new evidence is consistent with the factor-of-2 equator-to-pole paleointensity signature of a geocentric axial dipole field and also indicates that the time-averaged field is considerably weaker than the present-day field. The resulting dipole moment provides a new calibration standard for cosmogenic isotope production rates and suggests that the present decrease in geomagnetic field intensity may simply be a return to a more average magnitude rather than a harbinger of a polarity reversal.

Abstract

The geomagnetic field is predominantly dipolar today, and high-fidelity paleomagnetic mean directions from all over the globe strongly support the geocentric axial dipole (GAD) hypothesis for the past few million years. However, the bulk of paleointensity data fails to coincide with the axial dipole prediction of a factor-of-2 equator-to-pole increase in mean field strength, leaving the core dynamo process an enigma. Here, we obtain a multidomain-corrected Pliocene–Pleistocene average paleointensity of 21.6 ± 11.0 µT recorded by 27 lava flows from the Galapagos Archipelago near the Equator. Our new result in conjunction with a published comprehensive study of single-domain–behaved paleointensities from Antarctica (33.4 ± 13.9 µT) that also correspond to GAD directions suggests that the overall average paleomagnetic field over the past few million years has indeed been dominantly dipolar in intensity yet only ∼60% of the present-day field strength, with a long-term average virtual axial dipole magnetic moment of the Earth of only 4.9 ± 2.4 × 1022 A⋅m2.

Bacteria could help tackle the growing mountains of e-waste that plague the planet. Although researchers are a long way from optimizing the approach, some are already confident enough to pursue commercial ventures.

Holographic acoustic tweezers, in which ultrasonic waves produced by arrays of sound emitters are used to individually manipulate up to 25 millimeter-sized particles in three dimensions, could be used to create 3D displays consisting of levitating physical voxels.